By plugin you can add only one webform on sidebar. But
You can also just put in script on your site:
<script type="text/javascript" src="http://app.getresponse.com/view_webform.js?wid=WEBFORM_ID"></script>
wherever you want to display webform.

If you want to have more than one webform I recommend use only one in js
other you can implement by using HTML code.